Mechanical properties of ultrafine-grained aluminum in the temperature range 4.2–300 K

The tensile curves of ultrafine-grained (UFG) aluminum structured by high pressure torsion (HPT) technique have been obtained at 4.2 and 77 K for the first time as well as the temperature dependence of its yield strength in the range 4.2–300 K. The analysis of the results in correlation with microstructure parameters and comparison with the results of such studies for UFG aluminum structured by equal-channel angular pressing (ECAP) technique has been performed. It has been shown that the HPT-processed aluminum has a significantly higher yield strength at low temperatures than the ECAP-processed aluminum. Combination of high strength and plasticity (440 MPa and 55%, respectively) was obtained at 4.2 K, which makes this material attractive for practical use at low temperatures. The analysis of the obtained results indicates that, at room and low (77 K) temperatures, the plasticity of the UFG aluminum with a grain size less than 1 $\mu$m largely depends on the nature of the grain size distribution, as well as on the type and state of the grain boundaries (equilibrium or nonequilibrium), which opens up prospects for controlling the value of plasticity by creating a given microstructural design while maintaining a high level of strength of ultrafine-grained materials.